Why would "java.lang.IllegalStateException: The resource configuration is not modifiable in this context." appear deploying Jersey app?

Question

I have created an app implementing REST services locally using:

Eclipse Indigo Jersey 2.4 Tomcat 7.0.47

When running locally using Eclipse, the services work OK, but when deploying my WAR file, I get the following exception when trying to do a GET to one of the services URL:

HTTP Status 500 - Servlet.init() for servlet com.app.rest.MyResourceConfig threw exception

type Exception report

message Servlet.init() for servlet com.app.rest.MyResourceConfig threw exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet.init() for servlet com.app.rest.MyResourceConfig threw exception
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    java.lang.Thread.run(Thread.java:662)

root cause

java.lang.IllegalStateException: The resource configuration is not modifiable in this context.
    org.glassfish.jersey.server.ResourceConfig$ImmutableState.register(ResourceConfig.java:270)
    org.glassfish.jersey.server.ResourceConfig$ImmutableState.register(ResourceConfig.java:218)
    org.glassfish.jersey.server.ResourceConfig.register(ResourceConfig.java:448)
    org.glassfish.jersey.servlet.WebComponent.<init>(WebComponent.java:300)
    org.glassfish.jersey.servlet.ServletContainer.init(ServletContainer.java:167)
    org.glassfish.jersey.servlet.ServletContainer.init(ServletContainer.java:349)
    javax.servlet.GenericServlet.init(GenericServlet.java:160)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    java.lang.Thread.run(Thread.java:662)

I've been unable to find yet a root cause and my only suspicion is that it might be a missing running dependency or some other configuration in Eclipse that differ from my own local Tomcat server environment and the Tomcat at remote server.

My code at the resource configuration class is:

package com.app.rest;

import javax.ws.rs.ApplicationPath;
import org.glassfish.jersey.server.ResourceConfig;

import com.app.rest.services.RunDetailsService;
import com.app.rest.services.RunHistoryService;
import com.app.rest.services.RunPollService;
import com.app.rest.services.RunTestService;


@ApplicationPath("api")
public class MyResourceConfig extends ResourceConfig {

    public MyResourceConfig() {
        register(RunHistoryService.class).
        register(RunTestService.class).
        register(RunDetailsService.class).
        register(RunPollService.class);     
    }   
}

What do you think would be a possible cause?

Answer 1

One possible cause is that you have two or more applicable mappings for that URL call.

For example:

@Path("/{myParam}")

And somewhere else:

@Path("/{differentParam}")

Now Jersey have no way of telling what method is actually supposed to be called and gives this error.